Bolt preload and externally applied tension load 2

[Kristina Sornikova]

Dear bolt experts, I confuse about bolt preload and externally applied tension load.

If a bolt is installed, I use a torque to preload joint, then there is weight applied externally, will this load add to bolt tension load or not until it is more than preload?

Thank you...

 

[btrueblood]

The latter, mostly. The longer answer is "it can get complicated". Read Shigley's Mechanical Engineering Design, or a similar mechanical engineering design textbook. Realize too, that in aerospace a lot of times you have a material elastic modulus difference between the fastener and the mating materials, which goes towards that "it can get complicted" statement.

 

[ingparada]

tengo entendido que los esfuerzos de tensión en los conectores comprimen los elementos conectados al aplicar el pre-esfuerzo y al haber una carga externa en tensión no habrá ningún esfuerzo adicional sobre los conectores mientras las partes conectadas no comience a deformarse.

 

[klaus.]

No...the external tension ist NOT added to the preload....otherwise prestressed bolts won't work

The external tenssion load will reduce the pressure due to pretension

 

[desertfox]

hi Kristina

As others have said the external load does not add directly to the preload, the external load is added proportionally to both the elasticity of the parts clamped between the bolt and the elasticity of the bolt itself.
normally the jointed part are a lot stiffer then the bolt and some most of the external load is taken up reducing the pressure between the clamped parts.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[chicopee]

To further simplify desertfox statement, if the external load exceed the preload then there is no more pressure between the bolted parts; and part separation could take place when external load exceed preload.

 

[Agent666]

You can demonstrate the concept practically using a simply model with a rubber band analogy:-

Take a rubber band and stretch it around two objects that are in contact. To add to the preload (i.e. to move the objects apart and stretch the rubber band more) you need to provide a force greater than the force holding the objects together. The rubber band is the bolt and the objects are the two plies being bolted together. Rubber band does not see any additional force until you overcome the tension in the rubber bands holding the objects together.

 

[Kristina Sornikova]

All great feedback thank you all.. For reference, Shigley and Mishke had similar note for external load no adding to preload if less than preload.